1. Field of the Invention
The present invention relates to a shutter control device suitable for use when tripping a shutter of, e.g., a single-lens reflex camera.
2. Related Background Art
FIG. 1 is a sectional view showing a configuration in section by way of one example of a prior art single-lens reflex camera. Referring to FIG. 1, a subject image passing through a photographing lens 1 is reflected by a mirror 2 toward a viewing optical system 3 and confirmed by a finder 4. When photographed, the mirror 2 retreats to a position (retreat position) indicated by a broken line in the Figure. Thereafter, a shutter 5 constructed of leading and trailing curtains is sequentially tripped, thus effecting an exposure.
A conventional method of electrically setting timings of the retreating action of the mirror 2 and of the tripping action of the shutter 5 is classified mainly into the following two kinds of methods.
According to the first method, a switch changed over interlocking with the retreating action of the mirror 2 is provided. The retreat of the mirror 2 is confirmed from an output of this switch, and the tripping of the shutter 5 is started.
According to the second method, a timer is actuated simultaneously when performing a release operation. After a predetermined time has elapsed (irrespective of the action of the mirror 2), the tripping of the shutter 5 is started.
The prior art discussed above, presents the following problems.
The mirror 2 is driven by a mechanism portion consisting of springs, a motor, etc., and hence a retreat time of the mirror 2 changes with the operational fluctuations of such a mechanism. Therefore, according to the first method, the tripping timing of the shutter 5 depends on the action of the mirror 2. A time (hereinafter called a release time lag) from the release operation to the tripping of the shutter 5 varies infinitesimally per photographing action. This results in such a problem that a shutter chance is hard to capture precisely. Further, during photographing under such conditions that an excessive gravity is applied (e.g., as in an airplane when taking off and landing or an automobile in motion), if the gravity is applied in such a direction as to reduce the retreat time of the mirror 2, the shutter 5 is tripped before the aperture is stopped down. Consequently, there arises a problem of inducing an overexposure exceeding an intended exposure.
The second method has no fluctuation in terms of the release time lag as seen in the first method. Under the conditions, where the gravity is applied in such a direction as to extend the retreating time of the mirror 2, however, it may happen that the shutter 5 is tripped before the retreat of the mirror 2 is completed. In this instance, the mirror 2 is positioned within a photographing picture, and it follows that the photographing picture is vignetted.
To eliminate this problem, the release time lag may be set by giving a sufficient allowance time to the retreating time of the mirror 2. The release time lag should be, however, reduced to the greatest possible degree so as not to lose a shutter chance during normal photographing. Accordingly, the extension of the release time lag is not an adequate solution for the problem described above.